The “grey zone” or how to avoid the binary constraint of decision-making

Excerpt

In this issue of the Journal, Vos et al. report on the accuracy of pulse pressure variation (PPV), stroke volume variation (SVV), and stroke volume index (SVI) to predict fluid responsiveness at multiple thresholds.1 In their study, they show that the threshold used to define fluid responsiveness impacts the predictive value of these indices and the range of their zones for decision-making (i.e., the “grey zone”)—the lower the threshold for the definition of fluid responsiveness, the lower the predictive value and the wider the grey zone. Although these results are not completely surprising (i.e., how one defines an outcome generally impacts the accuracy of the tools used to predict that outcome) or entirely new (i.e., the concept of using a PPV grey zone - though perhaps not these authors’ precise definition - for understanding fluid responsiveness had already been reported),2 they nevertheless remind us of the importance of using the grey zone methodology when approaching any diagnostic tool (such as PPV and SVV). Accordingly, this editorial serves as a reminder of the relevance, impact, and global meaning of the grey zone for diagnostic tools. …